Abstract
Above ground biomass (AGB) is a parameter commonly used for assessment of grassland systems. Destructive AGB measurements, although accurate, are time consuming and are not easily undertaken on a repeat basis or over large areas. Structure-from-Motion (SfM) photogrammetry and Terrestrial Laser Scanning (TLS) are two technologies that have the potential to yield precise 3D structural measurements of vegetation quite rapidly. Recent advances have led to the successful application of TLS and SfM in woody biomass estimation, but application in natural grassland systems remains largely untested. The potential of these techniques for AGB estimation is examined considering 11 grass plots with a range of biomass in South Dakota, USA. Volume metrics extracted from the TLS and SfM 3D point clouds, and also conventional disc pasture meter settling heights, were compared to destructively harvested AGB total (grass and litter) and AGB grass plot measurements. Although the disc pasture meter was the most rapid method, it was less effective in AGB estimation (AGBgrass r2 = 0.42, AGBtotal r2 = 0.32) than the TLS (AGBgrass r2 = 0.46, AGBtotal r2 = 0.57) or SfM (AGBgrass r2 = 0.54, AGBtotal r2 = 0.72) which both demonstrated their utility for rapid AGB estimation of grass systems.
Highlights
Quantification of the above ground biomass (AGB, units g m−2 ) of grasslands is important for a number of applications including pasture management [1], wildlife habitat monitoring [2,3], fire management [4,5], carbon storage [6,7], and understanding the implications of biophysical and ecological processes that influence grass production [8,9]
This study examines the potential of Terrestrial Laser Scanning (TLS) and SfM photogrammetry for rapid nondestructive estimation of grass Above ground biomass (AGB)
The correspondence between the disc pasture meter settling heights and the destructively harvested AGB described in this study were lower than reported in some literature, which may be due to site and grass differences [12,57]
Summary
Quantification of the above ground biomass (AGB, units g m−2 ) of grasslands is important for a number of applications including pasture management [1], wildlife habitat monitoring [2,3], fire management [4,5], carbon storage [6,7], and understanding the implications of biophysical and ecological processes that influence grass production [8,9]. Conventional grassland AGB estimation methods rely on allometric relationships established between destructively harvested AGB plot data and a grass structural property, such as the grass height, that can be measured elsewhere [10,11]. A long established grass AGB estimation method is the disc pasture meter which allometrically relates the settling height of a weighted disc on a grassland plot to the AGB beneath it [12,13]. Three dimensional (3D) point clouds of the vegetation surface are derived from laser scans and allow the reconstruction of quantitative 3D vegetation models [14,15,16] that, with knowledge of the vegetation density, enable biomass estimation without allometric information [17,18]
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